Bacillus thuringiensis (B.t.) produces an insect toxin designated as .delta.-endotoxin. It is synthesized by the B.t. sporulating cell. The toxin, upon being ingested in its crystalline form by susceptible insect larvae, is transformed into biologically active moieties by the insect gut juice proteases. The primary target is insect cells of the gut epithelium, which are rapidly destroyed.
The reported activity spectrum of B.t. covers insect species within the order Lepidoptera, many of which are major pests in agriculture and forestry. The activity spectrum also includes the insect order Diptera, which includes mosquitos and black flies. See Couch, T. L. (1980) "Mosquito Pathogenicity of Bacillus thuringiensis var. israelensis," Developments in Industrial Microbiology 22:61-76; Beegle, C. C., (1978) "Use of Entomogenous Bacteria in Agroecosystems," Developments in Industrial Microbiology 20:97-104. Krieg, et al., Z. ang. Ent. (1983) 96:500-508, describe a B.t. isolate named Bacillus thuringiensis var. tenebrionis, which is reportedly active against two beetles in the order Coleoptera. These are the colorado potato beetle, Leptinotarsa decemlineata, and Agelastica alni.
In European Patent Application 0 202 739 there is disclosed a novel B.t. isolate active against Coleoptera. It is known as B. thuringiensis var. san diego (B.t.sd.). U.S. Pat. No. 4,966,765 discloses the coleopteran-active Bacillus thuringiensis isolate B.t. PS86B1.
Insects in the family Scarabaeidae (Scarabs) constitute a serious pest control problem, especially when destructive larval stage insects infest high value turf found in golf courses, playing fields and lawns. The larvae of many species also attack grains, tuberous crops, and ornamentals. Larvae are called "white grubs" or "chafer grubs" and can be found in decaying organic matter (rotting leaves, manure, etc.) or 2-10 cm. deep in soil where they consume the plant roots. In turf infested areas there can be as many as 30 grubs per square foot. The damage caused by an infestation becomes most apparent in the fall when the third instar grubs are feeding. Adult beetles of some Scarab species will feed on a wide variety of vegetative host, damaging foliage, fruit and flowers of woody and herbaceous plants. In the U.S. and Europe, populations of larvae and adults have developed resistance to chemical insecticides such as the organochlorines and DDT.
Several Scarab pests are of economic importance. Particularly important pests in the U.S., especially east of the Rockies, but also in the Western States, are the Masked Chafers, Cyclocephala sp. In the east, the Northern Masked Chafer, C. borealis, and the Southern Masked Chafer, C. immaculata, are common pests, while in California C. hirta and C. pasadenae are present. Also, in the U.S., especially in the area east of the rockies, infestations of Japanese beetles Popillia sp., May or June beetles Phyllophaga sp., black turfgrass beetles Ataenius sp., European chafers Rhizotrogus sp. tend to necessitate the greatest amount of insecticide treatments. Other important Scarab pests in the U.S. can be quite damaging but localized such as with Oriental beetles Anomala sp., hoplia chafers Hoplia sp., green June beetle Cotinis sp., and Asiatic garden beetles Maladera sp. Several Scarabs not present the U.S., are of economic importance in Europe including rose chafers Cetonia sp., cockchafers Melolontha sp., flower beetles Adoretus sp., and garden chafers Phyllopertha sp. The green June beetles, Cotinis sp., can cause serious damage where populations become abundant. The adults are attracted to ripening fruit and will devour figs, peaches and other thin skinned fruit while on the tree. Larvae are attracted to decaying organic matter and most commonly become pests in turf or fields which have been fertilized with manure. The feeding and tunnelling of the large larvae can become disruptive. The Eastern Green June Beetle Cotinis nitida is present in the mid-western and eastern states, while the Green June Beetle C. mutabilis occurs in many of the western states.